1/4"-20 is 20 threads per inch. Each rotation of this screw will yield .050" displacement. You have to rotate it 20 times to move one inch. Divide 1 inch by the number of threads to get the displacement. 1/20=0.050".
So - if you want to get just 50IPM from your machine, you would have to spin this screw 1,000 RPM, right? 20 turns per inch, 50 inches to travel = 1,000 turns per minute.
How big is your machine going to be? What speeds do you want to reach?